A. Field of the Invention
The invention relates to mask construction techniques employed in photographic fabrication of microminiature electronic devices, particularly those devices requiring the use of high resolution photolithographic techniques.
B. Description of the Prior Art
Pattern generation in planar thin film overlays is usually accomplished by reproducing the pattern (or its negative) in a photosensitive resist applied to the film's surface. In order to obtain accurate delineation of the pattern, positive contact between the pattern mask and the photoresist surface is essential. Build-ups of photoresist material often occur around the perimeter of a substrate and thereby prevent contact between the pattern mask and the surface of the photoresist. Thus, the precise masking ability of the mask apparatus is of great importance. In the prior art, methods for making precise mask apparatus range from chemical build-up of the mask to mechanical construction thereof. Chemically fabricated masks require a number of processing steps both in the application of the mask and in the removal thereof. Mechanical masks therefore present certain advantages, such as reduction of fabrication time, reuseability, etc. However, mechanical masks in high resolution work are susceptible to the aforementioned difficulties associated with excessive photoresist deposits around the perimeter of a substrate which prevent intimate contact between the masking pattern and the surface of the substrate. The present invention provides a method for fabricating a mechanical mask which avoids these contact problems, thereby rendering the use of mechanical masks more acceptable in high resolution photolithographic production of microelectronic devices. A particular advantage of the present method is that use of the present method improves yields in mask-to-resist pattern transfer without surface preparation.